Detectors Flashcards
Which carrier gas is most commonly used with TCD and why?
He - high thermal conductivity
What is the purpose of the reference cell in TCD?
only MP passes through reference cell and it measures a) variations in flow rate b) electric surges c) carrier gas P all three can affect filament resistance
What is the rule of thumb with TCD?
greater change in T, greater TCD increase in [A] and velocity of the analyte also increase TC
What are the advantages of TCD?
universal response increasing sensitivity with decreasing T good linear and adequate sensitivity for many compounds Nondestructive
What type of compounds can be detected with FID?
organic
How does FID work?
sample is burned in a mixture of H2/air flame produces radicals which create a current that flows between a potential difference of two electrodes
What does sensitivity of FID depend on?
ion production is directly proportional to the number of carbon atoms entering the flame
Can inorganic compounds be detected by FID?
yes, but it needs to modified and is more commonly called Hydrogen Atmosphere flame ionization detector
Advantages to FID?
almost universal response to all organic compounds wide linear dynamic range higher sensitivity
What does ECD detector consist of?
outer source electrode(+) central collector electrode(-)
Why is the central collector electrode special?
it consists of a beta-radiation emitter, which emits electrons
What happens to the carrier gas as it flows through the ECD detector?
ionized by electrons resulting in the production of additional electrons e- + N2 –> 2e- + N2+
How does the ECD detector work?
there is a decrease in current which is a result of negatively charged molecular ions that are neutralized by the ionized nitrogen
What is the ECD sensitive to?
organics containing halogens, nitriles, carbonyl, and nitro groups
